"We're having a baby!" Jill tells PEOPLE exclusively. "We are so excited."

Jill, 23, and husband Derick, 25, who tied the knot on June 21 in Springdale, Arkansas, shared their first kiss in front of more than 1,000 family and friends and then celebrated with them at a reception.

The couple's wedding will be featured on TLC's hit reality show19 Kids and Counting, during its new season that begins Sept. 2 (9 p.m. ET).

After taking several pregnancy tests that came back negative, Jill was persuaded by her sisters to take one of her mom Michelle's tests while she and Derick were visiting her parents' home. This test gave her a very different result – it was positive!

"It was surreal," says Derick. "We were shocked. Both of us are so excited."

The happy couple, who are due in March, have been having fun sharing their news with their family.

"About 30 days after Jill and Derick got married they gathered everyone in the living room and shared the news," Jim Bob, 49, tells PEOPLE. "Everyone was clapping and cheering, and we were in shock, too."

For much more on the couple's pregnancy and plans for a supersize family of their own – and exclusive details on her sister Jessa's romantic engagement to Ben Seewald – pick up this week's issue of PEOPLE, on newsstands Friday